Motion of a natural knee is kinematically complex. During a relatively broad range of flexion and extension, the articulating or bearing surfaces of a natural knee experience axial rotation, adduction, abduction, translation in the sagittal plane (rollback and sliding), and translation in the coronal plane. Knee joint prostheses, in combination with ligaments and muscles, attempt to duplicate this natural knee motion, as well as absorb and control forces generated during the range of flexion.
A knee joint prosthesis typically comprises a femoral component and a tibial component. The femoral component and the tibial component are designed to be surgically attached to the distal end of the femur and the proximal end of the tibia, respectively. The femoral component is further designed to cooperate with the tibial component in simulating the articulating motion of an anatomical knee joint.
There are known several types of knee prosthetics which are generally separated into two categories, first, regarding the amount of constraint or articulation allowed in the knee prosthetic joint. The types of knee prosthetics regarding constraint amount are cruciate retaining, posterior stabilized, and fully constrained. The cruciate retaining generally replaces only the articulating portions of the femur and the tibia when the soft tissue surrounding the knee can be saved or is not damaged. A posterior stabilized knee prosthetic is generally used when the posterior cruciate ligament needs to be resected due to damage or injury. Finally, the fully constrained knee prosthetic is used when almost all the soft tissue surrounding the knee needs to be resected or is no longer strong enough to perform the functions of the natural knee. Therefore, the cruciate retaining allows substantially all natural and uninjured motion of the knee.
The second category, and usable in each of the types of knees described above, are three different hinge or bearing mechanisms. The bearing mechanisms include a floating bearing, fixed bearing, and a hinge. The floating bearing is a bearing or meniscus replacement which is not affixed in any way to either the femoral component or the tibial component. It is simply a bearing between the femoral component and the tibial component and can move relative to either. This allows for greater muscle efficiency more closely simulating a natural knee. A fixed bearing, however, is fixed relative to the tibial component. Therefore, once the bearing is put in place, the femoral component rides on the bearing but the bearing does not move relative the tibial component. Finally, the hinged knee allows simple hinge movement from an extended to a flexed position. It is generally known in the art that any constrained knee prosthetic can be used with any bearing portion.
Soft tissue replacements or grafts may be implanted when soft tissue in a knee is injured or damaged and non-functioning. Generally, the articulating portions of the knee are satisfactory while the soft tissue ligaments and tendons surrounding the knee have been damaged due to injury or other causes. Therefore, it is only necessary to replace these damaged tendons and other soft tissues, rather than replacing the articulating portions of the knee joint. This is desirable because the natural knee joint provides the greatest range of motion and muscle efficiency, as opposed to prosthetic knee joints to date.
Although it is possible to more easily augment or retain the medial and lateral collateral ligaments in the knee and implant a knee prosthesis, this is generally difficult. A generally known knee prosthesis may possibly be used while including augmentation or implantation of medial and lateral collateral ligaments because these ligaments do not intersect the knee prosthetic. Therefore, a physician may be able to augment, such as tighten the medial or lateral ligaments, while also implanting a knee prosthetic.
It is not known, however, to provide a knee prosthetic, of any of the kinds commonly known, which can also be used with a soft tissue replacement procedure of the anterior cruciate or posterior cruciate ligaments. Rather, the art has proceeded in two divergent paths: one saving or resecting the soft tissue and choosing an appropriate knee prosthetic or two, simply replacing the soft tissue surrounding the knees. This reduces the choices to surgeons. Rather than allowing them to replace a damaged soft tissue portion with a graft and thereby needing a less constrained knee prosthetic. This is because knee prosthetics generally do not include clearances for soft tissue grafts that must intersect the articulating region of the knee.
Therefore, what is needed, is a knee prosthetic which can be used in conjunction with soft tissue replacement procedures to allow for greater abilities of surgeons to more closely replicate the natural knee with prosthetics. In particular, soft tissue replacements, such as anterior cruciate or posterior cruciate ligament replacements, are desirable to be used in a total knee replacement to provide for a more natural knee movement. Therefore, the physician would not need to choose to either attempt to save the soft tissue or replace it with a more constrained knee. The physician could resect all the soft tissue and then choose a more appropriate implant and replace the resected ligaments. In addition, using the soft tissue replacement techniques increases the ability of the prosthetic knee to more closely mimic the natural knee.